I have a Bendix AD-2 in a MCI-8 that needs rebuilding. The bottom casting has "12vdc" molded on it. Evidently, the heater wire was not hooked up when it was replaced. I would like to hook it up after I rebuild it but, if it is actually 12vdc, 24vdc would probably "smoke" it. Does anyone know how to tell what voltage the heater element requires? Maybe the impedance(ohms) of the element could be measured? Does anyone know what this value should be? I'd rather not replace the dryer if I don't have to. TIA, John

You can order the bottom plate from NAPA. I just ordered a replacement cartridge for my AD-2 dryer. You can find the parts on NAPAONLINE.com. Enter air dryer in the keyword field and press enter.You can find the part numbers at Bendix.com.

I'm not sure if the heater in the AD-2 is the same as the one in the AD-9 but if it is, the circuit will be open while at room temperature. The AD-9 unit is switched by an integral thermostat. Put that baby in the freezer before you take your measurement. FWIW this should be done each time ANY drier is serviced to be certain that they are working.

If I remember correctly, the AD-2 heater in the 8s and 9s are 24 volts and are connected to the passenger heater switch. I think that was an option, so it's likely someone added it to your coach after manufacture, and used a 12v unit. You could certainly tap 12v from the battery (probably already available in the front j-box). The schematic says there's a 3 amp fuse on the circuit, so it doesn't draw much current.